The Browns said -- minutes before they placed Garrett on the reserve/COVID-19 list -- they were informed of a player's positive test Friday morning.
"Contact tracing has been conducted and the individual has self-isolated," the Browns said in a statement. "He has not been in the facility all week and zero high-risk contacts have been identified."
Browns coach Kevin Stefanski said Thursday that Garrett was scheduled to return to the team Friday after he missed practice this week due to a previously unspecified illness.
The Browns also said the team facility will remain open and the team will practice Friday as scheduled. All player and coach meetings Friday morning took place remotely.
NFL players who are placed on the reserve/COVID-19 list on a Monday or Tuesday potentially can play Sunday if they record five consecutive days of negative tests. Garrett will not be able to accomplish that by the Browns' game against the Philadelphia Eagles on Sunday in Cleveland.
Garrett, 24, leads the NFL with 9.5 sacks and four forced fumbles in nine starts this season. The 6-foot-4, 272-pound defensive end also has 31 total tackles, 14 quarterback hits, seven tackles for a loss and two fumble recoveries in 2020.
On Wednesday, the Browns placed tackle Jack Conklin and kicker Cody Parkey on the reserve/COVID-19 list. The Browns closed the team facility Monday after a player tested positive for COVID-19. The team later that day placed fullback Andy Janovich on the reserve/COVID-19 list.
The Browns will face the Eagles at 1 p.m. EST on Sunday at FirstEnergy Stadium.
NFL commissioner Roger Goodell announced Wednesday that all 32 teams will move into the league's intensive protocol for COVID-19 starting Saturday for the remainder of the 2020 season.
The protocol requires teams to hold meetings virtually, unless they can be held outside or inside with a preapproved plan, and for players and staff members to submit negative tests from the previous day before they enter team facilities.
The NFL on Tuesday announced that monitoring testing results from Nov. 8 to 14 showed 17 new confirmed positive tests among players and 35 among other personnel. The league said 95 players and 175 staff members had confirmed positive cases from Aug. 1 to Saturday.